There is two totally different interpretation about the mechanism of the c-t transition of ZrO2 based ceramics. One, which is proposed by Prof.Heuer, is that the transition is resulted from the first order type and the other, which is proposed by the author, is second type. The first interpretation has been popular in the field of ZrO2 ceramics since the author's invited presentation at the international conference of ZrO2 held in Australia on 1992. At this conference the author has cleared up that many experimental results can not be interpretated from the standing point that the transition is the first type and has confirmed that there is no contradictions when that transition is thought to be second order type. Moreover the author has made clear that various experimental results are resulted from the vacancies of oxygen in the fluorite lattice structure. When the oxygen ions move from the idea position in the fluorite structure by the introduction of the oxygen vacancies, there is the possibility that the type of this transition is mistaken for the first type.